This invention relates to an electrical module which is adapted to be mounted in a hole of an associated panel or assembly plate.
Electrical modules or devices, such as information or command devices in the form of switches handles, illuminated displays, etc. are known from European Patent Document B 0 074 427. In the conventional state of the art, such electrical modules or devices are affixed individually or most often in rows next to each other and/or in superposed relationship relative to associated panels or assembly plates. The electrical devices project to both sides of the assembly plate through an opening therein. One side of the electrical device corresponding to the exterior of the assembly plate is its operating or display side, whereas the opposite backside includes the electrical hardware, such as electrical terminals, switches, wiring, etc. Such electrical devices are technically denoted command and information devices, and they include push-button switches, cam switches and pilot lights which collectively are utilized to move a switch to a specified state and display the specified switch state through an appropriate illuminated light bulb. For example, if the electrical device is a push-button switch, the electrical hardware is located at the backside of the assembly plate whereas the push-button and a display light is located at the front side of the assembly plate so that the push-button can be pressed and illuminated to indicate the "on" condition and the reverse thereof.
The assembly plate includes one or more generally circular bore holes to affix the electrical devices thereto. It is conventional, as reflected by the aforementioned prior art, to provide the bore hole with a radially inwardly opening generally rectangular slot or groove. A solid tongue or rib integral with a housing of the electrical device enters the rectangular groove and functions to align or seat the electrical device housing within and relative to a particular bore hole of the assembly plate. This is a mass-produced assembly which has been found quite practical because it offers on the one hand accurate location, proper seating and easy assembly; while on the other hand the electrical device is prevented from rotating which is particularly important if the electrical device is subject to stresses, as, for example, cam switches which are operated through a rotating drive handle.
The latter described circular bore hole and keyhole slot with an associated rib or key on the electrical device housing is not applicable in all fields and is not mass produced for export because some countries do not provide conventional assembly plate circular bore holes with a rectangular keyhole slot or groove. Obviously, in such instances it is impractical after the manufacture of a circular bore hole in an assembly plate to provide a rectangular keyhole slot or groove by, for example, manually filing or milling the assembly plate at a periphery of the circular bore hole before the individual electrical devices are installed. On the other hand, mass production also rules out making two types of electrical devices in the first instance and delivering each to a potential user. That is, it is cost-prohibitive to manufacture one type of electrical device housing with a rib or key and another without a rib or key and likewise to provide an assembly plate with and without a keyhole slot, respectively. Furthermore, if the conventional electrical devices with solid keys or ribs are installed into circular bore holes or perforations which do not have a keyhole slot or groove, then the housings of the electrical devices will be deformed or the assembly plates will be deformed or both at least locally. Such deformation could hamper the operation of the electrical device. Therefore, it has been found to be necessary to remove the rib or key from each electrical device housing before installation to prevent improper operation as might occur should the housing of the electrical device be deformed, as would occur if the key or rib were retained. However, the removal of such ribs is laborious and time-consuming considering that the material is normally a tough and hard plastic which cannot be readily cut or milled off. If an attempt is made to break-off the rib, the electrical device housing may be damaged. Moreover, such electrical devices are equipped with tightly fitting seals and efforts toward breaking the ribs present the danger of damaging the seals or preventing the same from being properly positioned. It has been suggested in this regard to mount an axial parallel positioning pin at a stop surface of a projection of the electrical device housing, such that the pin will enter the keyhole slot of the bore hole in one application, but if the keyhole slot is lacking, the pin is merely broken off and not utilized. However, this design does not afford adequate security against rotation of the electrical device and its housing because the positioning pin will be bent, broken or sheared off in normal operation and under rotary load.